Acta Veterinaria et Zootechnica Sinica ›› 2025, Vol. 56 ›› Issue (4): 1934-1946.doi: 10.11843/j.issn.0366-6964.2025.04.040

• Basic Veterinary Medicine • Previous Articles     Next Articles

Investigation of Heteroresistance and Its Mechanism of Staphylococcus aureus in Raw Milk

HE Xiaolan1(), ZHAO Yankun1,2, MENG Lu1, LIU Huimin1, GAO Jiaojiao2, ZHENG Nan1,*()   

  1. 1. Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing 100193, China
    2. Key Laboratory of Agro-Products Quality and Safety of Xinjiang, Ministry of Agriculture and Rural Affairs-Laboratory of Quality and Safety Risk Assessment for Agro-Products, Institute of Quality Standards & Testing Technology for Agro-Products, Xinjiang Academy of Agricultural Sciences, Urumqi 830091, China
  • Received:2024-03-14 Online:2025-04-23 Published:2025-04-28
  • Contact: ZHENG Nan E-mail:2460213483@qq.com;zhengnan@caas.cn

Abstract:

This experiment was conducted to study the drug resistances of Staphylococcus aureus isolated from raw milk, the prevalence of heteroresistance of Staphylococcus aureus and explore the mechanism of heteroresistance. Thirty-six Staphylococcus aureus isolates were isolated from 179 batches of raw milk collected from Northeast, North China, East China, South China, Northwest and Southwest. The sensitivity and resistance of Staphylococcus aureus were identified using broth microdilution method. The combination of disk diffusion method and E-test method was used to screen suspected heteroresistant strains from strains with sensitive phenotypes, and then the suspected heteroresistant strains were confirmed by Population analysis profiling(PAP). The stability of the heteroresistant phenotype after serial passage was measured. Finally, whole-genome sequencing and whole genome re-sequencing analysis were used to determine the heteroresistant mechanisms. The results showed that 36 strains of Staphylococcus aureus were resistant to β-lactam antibiotics, the resistant rate to ranges from 11.11% to 61.11%, and had high sensitivity to tetracycline and aminoglycoside antibiotics. 19 combinations of Staphylococcus aureus and antibiotics with heteroresistant were identified through initial screening, and it was confirmed that the 3 combinations exhibited heteroresistant phenotypes, of which only amoxicillin-clavulanate-J23 heteroresistant stabled after serial passage. This study demonstrates that S. aureus of raw milk origin is high resistant to β-lactam and quinolone antimicrobials. Heteroresistant mechanisms to amoxicillin-clavulanic acid are associated with blaZ and metal β-lactamase expression. Heteroresistant mechanisms to tetracyclines is associated with tetracycline efflux pumps and resistance proteins.

Key words: raw milk, S. aureus, heteroresistant, resistant subpopulations, whole-genome sequencing

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